1. Technical Field
The present invention relates to an ultrasonic device.
2. Related Art
Diaphragm-type ultrasonic sensors are conventionally known. In this type of ultrasonic sensor, a PZT ceramic thin film layer flanked by two electrodes is formed on one side of a diaphragm, and the electrical signals output from the electrodes are used to detect ultrasonic waves (see, for example, Japanese Laid-Open Patent Application 2006-319945).
In the ultrasonic sensor in Japanese Laid-Open Patent Application 2006-319945, buckling caused by internal stress of the diaphragm, which has a multi-layered film, is exploited to apply pressure in the upper direction of the diaphragm, thereby statically deflecting the diaphragm so that the diaphragm becomes convex in the upper direction.